1. Field of the Invention
The present invention relates to a contact type measuring apparatus including a measuring probe having a contact tip provided at a tip end portion thereof, which is brought into contact with a surface of an object to be measured, to thereby measure a three-dimensional shape.
2. Description of the Related Art
As a three-dimensional shape measuring method of obtaining data on coordinates and a shape of a surface of an object to be measured that has a three-dimensional structure, there is known a measuring method in which a probe is moved along the surface of the object to be measured while being in pressure-contact with the surface of the object to be measured by a predetermined contact force, to thereby measure a surface shape of the object to be measured based on a moving position of the probe.
In the conventional three-dimensional shape measuring method, as disclosed in Japanese Patent Application Laid-Open No. H06-265340, an air bearing is employed so that a probe shaft is provided so as to be movable in a vertical direction, to thereby allow the probe to support its own weight via a spring. With this configuration, the measurement may be performed with a minimum contact force, which prevents the object to be measured from being damaged by a weight applied along with the measurement or from being displaced from the mounted position.
However, according to the configuration disclosed in Japanese Patent Application Laid-Open No. H06-265340, there is a limit in reducing the contact force for pressing the probe against the object to be measured. In view of this, as disclosed in Japanese Patent Application Laid-Open No. 2004-012244, there is a method of measuring a shape of a microfabricated object to be measured by using a probe which employs, as a contact tip, a fine particle trapped by an optical radiation pressure of a laser beam, without through a shaft which is a rigid body.
The laser beam, which is condensed by a condensing lens and applied to the fine particle, is reflected and refracted at an interface between the fine particle and outside air, and therefore generates an optical radiation pressure. The optical radiation pressure thus generated results in a resultant force (trapping force) in a vertically upward direction that is equal to or larger than the self weight of the fine particle, and the resultant force acts on the fine particle, to thereby hold the fine particle. As described above, the fine particle held by the optical radiation pressure is used as the contact tip, to thereby realize a contact force on the order of 10−5 N.
The method disclosed in Japanese Patent Application Laid-Open No. 2004-012244 may be effective at reducing the contact force. However, it is necessary to first trap the fine particle that is provided in advance as the contact tip, before starting measurement.
Further, in order to generate the resultant force in a vertically upward direction which exceeds the self weight of the fine particle by using the optical radiation pressure, it is necessary to condense light on the fine particle at a large angle with respect to an optical axis of the detection optical system. Accordingly, when measuring a rectangular groove shape, the object to be measured blocks light that should be applied to the fine particle, with the result that the fine particle may not be held by the optical radiation pressure.
Further, the fine particle is assumed to be transparent and spherical, and hence illuminating light passes through the fine particle and leaks therefrom. The transmitted light reaches the object to be measured and is reflected when the fine particle is brought closer to the object to be measured. As a result, the illuminating light and the reflected light interfere with each other to change the optical radiation pressure, which leads to measurement error.